This section provides background information related to the present disclosure which is not necessarily prior art.
A data center is a room containing a collection of electronic equipment, such as computer servers. Data centers and the equipment contained therein typically have optimal environmental operating conditions, temperature and humidity in particular. A climate control system maintains the proper temperature and humidity in the data center.
The climate control system includes a cooling system that cools air and provides the cooled air to the data center. The cooling system may include air conditioning units, such as computer room air handling (CRAH) or computer room air conditioning (CRAC) units that cool the air that is provided to the data center. The data center may have a raised floor and the cooled air introduced into the data center through vents in the raised floor. The raised floor may be constructed to provide a plenum between the cold air outlet of the CRAH (or CRAHs) or CRAC (or CRACs) and the vents in the raised floor, or a separate plenum such as a duct may be used.
The data center could also have a hard floor. The CRACS may, for example, be arranged in the rows of the electronic equipment, may be disposed with their cool air supply facing respective cold aisles, or be disposed along walls of the data center. The equipment racks in the data center may be arranged in a hot aisle/cold aisle configuration with the equipment racks arranged in rows. The cold air inlets of the racks, typically at the front of the racks, in one row face the cold air inlets of the racks in a row across a cold aisle, and the hot air outlets of the racks in one row face the hot air outlets of the racks in a row across a hot aisle.
One type of cooling system uses a pumped refrigerant cooling unit, such as the cooling units used in the XD System available from Liebert Corporation of Columbus, Ohio. The Liebert XD System has two cooling loops, that may also be referred to as cooling circuits or cycles. A primary loop uses chilled water or a refrigerant, such as R407C and a secondary loop uses a pumped refrigerant, such as R134a. The primary loop includes a fluid to fluid heat exchanger to cool the pumped refrigerant circulating in the secondary loop. The secondary loop includes one or more phase change cooling modules having a fluid to air heat exchanger through which the pumped refrigerant is circulated to cool air flowing across the heat exchanger. The heat exchanger may typically include an evaporator coil and a flow regulator or an expansion valve, in accordance with the particular design.
Basic schematics for the two cooling loops (or cycles) of the Liebert XD System are shown and described in U.S. Ser. No. 10/904,889 for “Cooling System for High Density Heat Load,” the entire disclosure of which is incorporated herein by reference. FIGS. 1 and 2 of this application are included herein as FIGS. 1 and 2 along with the accompanying description from this application.
Referring to FIGS. 1 and 2, the disclosed cooling system 10 includes a first cooling cycle 12 (the primary cooling loop) in thermal communication with a second cycle 14 (the secondary cooling loop). The disclosed cooling system 10 also includes a control system 90. Both the first and second cycles 12 and 14 include independent working fluids. The working fluid in the second cycle is any volatile fluid suitable for use as a conventional refrigerant, including but not limited to chlorofluorocarbons (CFCs), hydro fluorocarbons (HFCs), or hydrochloro-fluorocarbons (HCFCs). Use of a volatile working fluid eliminates using water located above sensitive equipment, as is sometimes done in conventional systems for cooling computer room. The second cycle 14 includes a pump 20, one or more first heat exchangers (evaporators) 30, a second heat exchanger 40, and piping to interconnect the various components of the second cycle 14. The second cycle 14 is not a vapor compression refrigeration system. Instead, the second cycle 14 uses the pump 20 instead of a compressor to circulate a volatile working fluid for removing heat from a heat load. The pump 20 is preferably capable of pumping the volatile working fluid throughout the second cooling cycle 14 and is preferably controlled by the control system implemented by controller 90.
The first heat exchanger 30 is an air-to-fluid heat exchanger that removes heat from the heat load (not shown) to the second working fluid as the second working fluid passes through the second fluid path in first heat exchanger 30. For example, the air-to-fluid heat exchanger 30 can include a plurality of tubes for the working fluid arranged to allow warm air to pass therebetween. It will be appreciated that a number of air-to-fluid heat exchangers known in the art can be used with the disclosed cooling system 10. A flow regulator 32 can be connected between the piping 22 and the inlet of the evaporator 30 to regulate the flow of working fluid into the evaporator 30. The flow regulator 32 can be any type of device for regulating flow in the cooling system 10. The flow regulator 32 preferably maintains a constant output flow independent of the inlet pressure over the operating pressure range of the system. In the embodiment of FIGS. 1 and 2, the second cycle 14 includes a plurality of evaporators 30 and flow regulators 32 connected to the piping 22. However, the disclosed system can have one or more than one evaporator 30 and flow regulators 32 connected to the piping 22.
The second heat exchanger 40 is a fluid-to-fluid heat exchanger that transfers heat from the second working fluid to the first cycle 12. It will be appreciated that a number of fluid-to-fluid heat exchangers known in the art can be used with the disclosed cooling system 10. For example, the fluid-to-fluid heat exchanger 40 can include a plurality of tubes for one fluid positioned in a chamber or shell containing a second fluid. A coaxial (“tube-in-tube”) exchanger would also be suitable. In certain embodiments, it is preferred to use a plate heat exchanger. The second cycle 14 can also include a receiver 50 connected to the outlet piping 46 of the second heat exchanger 40 by a bypass line 52. The receiver 50 may store and accumulate the working fluid in the second cycle 14 to allow for changes in the temperature and heat load.
In one embodiment, the air-to-fluid heat exchanger 30 can be used to cool a room holding computer equipment. For example, a fan 34 can draw air from the room (heat load) through the heat exchanger 30 where the second working fluid absorbs heat from the air. In another embodiment, the air-to-fluid heat exchanger 30 can be used to directly remove heat from electronic equipment (heat load) that generates the heat by mounting the heat exchanger 30 on or close to the equipment. For example, electronic equipment is typically contained in an enclosure (not shown). The heat exchanger 30 can mount to the enclosure, and fans 34 can draw air from the enclosure through the heat exchanger 30. Alternatively, the first exchanger 30 may be in direct thermal contact with the heat source (e.g. a cold plate). It will be appreciated by those skilled in the art that the heat transfer rates, sizes, and other design variables of the components of the disclosed cooling system 10 depend on the size of the disclosed cooling system 10, the magnitude of the heat load to be managed, and on other details of the particular implementation.
In the embodiment of the disclosed cooling system 10 depicted in FIG. 1, the first cycle 12 includes a chilled water cycle 60 connected to the fluid-to-fluid heat exchanger 40 of the second cycle 14. In particular, the second heat exchanger 40 has first and second portions or fluid paths 42 and 44 in thermal communication with one another. The second path 42 for the volatile working fluid is connected between the first heat exchanger 30 and the pump 20. The first fluid path 44 is connected to the chilled water cycle 60. The chilled water cycle 60 may be similar to those known in the art. The chilled water system 60 includes a first working fluid that absorbs heat from the second working fluid passing through the fluid-to-fluid heat exchanger 40. The first working fluid is then chilled by techniques known in the art for a conventional chilled water cycle. In general, the first working fluid can be either volatile or non-volatile. For example, in the embodiment of FIG. 1, the first working fluid can be water, glycol, or mixtures thereof. Therefore, the embodiment of the second cycle 14 in FIG. 1 can be constructed as an independent unit that houses the pump 20, air-to-fluid heat exchanger 30, and fluid-to-fluid heat exchanger 40 and can be connected to an existing chilled water service that is available in the building housing the equipment to be cooled, for example.
In the embodiment of the disclosed cooling system 10 in FIG. 2, the second cycle 14 is substantially the same as that described above. However, the first cycle 12 includes a vapor compression refrigeration system 70 connected to the first portion or flow path 44 of heat exchanger 40 of the second cycle 14. Instead of using chilled water to remove the heat from the second cycle 14 as in the embodiment of FIG. 1, the refrigeration system 70 in FIG. 2 is directly connected to or is the “other half” of the fluid-to-fluid heat exchanger 40. The vapor compression refrigeration system 70 can be substantially similar to those known in the art. An exemplary vapor compression refrigeration system 70 includes a compressor 74, a condenser 76, and an expansion device 78. Piping 72 connects these components to one another and to the first flow path 44 of the heat exchanger 40.
The vapor compression refrigeration system 70 removes heat from the second working fluid passing through the second heat exchanger 40 by absorbing heat from the exchanger 40 with a first working fluid and expelling that heat to the environment (not shown). The first working fluid can be volatile. For example, in the embodiment of FIG. 2, the first working fluid can be any conventional chemical refrigerant, including but not limited to chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), or hydrochloro-fluorocarbons (HCFCs). The expansion device 78 can be a valve, orifice or other apparatus known to those skilled in the art to produce a pressure drop in the working fluid passing therethrough. The compressor 74 can be any type of compressor known in the art to be suitable for refrigerant service such as reciprocating compressors, scroll compressors, or the like. In the embodiment depicted in FIG. 2, the cooling system 10 is self-contained. For example, the vapor compression refrigeration system 70 can be part of a single unit that also houses pump 20 and fluid-to-fluid heat exchanger 30.
During operation of the disclosed system, pump 20 moves the working fluid via piping 22 to the air-to-fluid heat exchanger 30. Pumping increases the pressure of the working fluid, while its enthalpy remains substantially the same. The pumped working fluid can then enter the air-to-fluid heat exchanger or evaporator 30 of the second cycle 14. A fan 34 can draw air from the heat load through the heat exchanger 30. As the warm air from the heat load (not shown) enters the air-to-fluid heat exchanger 30, the volatile working fluid absorbs the heat. As the fluid warms through the heat exchanger, some of the volatile working fluid will evaporate. In a fully loaded system 10, the fluid leaving the first heat exchanger 30 will be a substantially saturated vapor. The vapor flows from the heat exchanger 30 through the piping 36 to the fluid-to-fluid heat exchanger 40. In the piping or return line 36, the working fluid is substantially in the vapor state, and the pressure of the fluid drops while its enthalpy remains substantially constant. At the fluid-to-fluid heat exchanger 40, the vapor in the second fluid path 42 is condensed by transferring heat to the first, colder fluid of the first cycle 12 in the first fluid path 44. The condensed working fluid leaves the heat exchanger 40 via piping 46 and enters the pump 20, where the second cycle 14 can be repeated.
The first cooling cycle 12 operates in conjunction with second cycle 14 to remove heat from the second cycle 14 by absorbing the heat from the second working fluid into the first working fluid and rejecting the heat to the environment (not shown). As noted above, the first cycle 12 can include a chilled water system 60 as shown in FIG. 1 or a vapor compression refrigeration system 70 as shown in FIG. 2. During operation of chilled water system 60 in FIG. 1, for example, a first working fluid can flow through the first fluid path 44 of heat exchanger 40 and can be cooled in a cooling tower (not shown). During operation of refrigeration system 70 in FIG. 2, for example, the first working fluid passes through the first portion 44 of fluid-to-fluid heat exchanger 40 and absorbs heat from the volatile fluid in the second cycle 14. The working fluid evaporates in the process. The vapor travels to the compressor 74 where the working fluid is compressed. The compressor 74 can be a reciprocating, scroll or other type of compressor known in the art. After compression, the working fluid travels through a discharge line to the condenser 76, where heat from the working fluid is dissipated to an external heat sink, e.g., the outdoor environment. Upon leaving condenser 76, refrigerant flows through a liquid line to expansion device 78. As the refrigerant passes through the expansion device 78, the first working fluid experiences a pressure drop. Upon leaving expansion device 78, the working fluid flows through the first fluid path of fluid-to-fluid heat exchanger 40, which acts as an evaporator for the refrigeration cycle 70.
Data center providers are continually seeking increased reliability and up time from climate control systems. Therefore, data center providers continually desire improved redundancy in the climate control systems to guard against unnecessary down time of the cooled electronic equipment due to unexpected interruption in operation of the climate control systems. One mode of redundancy is to replicate each element of a cooling system, such as the first cooling cycle 12 and the second cooling cycle 14. Such complete redundancy can be prohibitively expensive and greatly complicates the design, implementation, and control of the cooling systems. In various configurations, redundancy may include implementation of a cooling loop, including a second, reduced implementation of a second cooling cycle 14 such as shown in FIGS. 1 and 2. The reduced redundancy could include a second pump unit 20 and half of the heat exchangers provided in the primary cooling system. Implementing this redundant system would also require the associated plumbing and controls. Accordingly, an approximate cost of such a system could be in the range of 50% of the total cost of the base cooling load.
Another approach to redundancy in order to minimize equipment can include over-provisioning the environment by deploying cooling modules in complicated, interweaved schemes. Failure of one cooling loop can then be covered by other cooling loops interwoven into the zone of the failed one cooling loop. Such over provisioning again provides increased cost to the consumer which includes extra pumps, cooling modules, plumbing, piping and control systems over conventional configurations shown in FIGS. 1 and 2.